ושחט, “he will slaughter, etc.” the Torah used the singular mode as ordinarily one person performs that act. On the other hand, when describing the steps following the act of slaughtering, the Torah uses the plural mode, as a number of priests are usually involved in that.

את בן הבקר, “the bullock;” the expression: בן הבקר implies that the animal is male and young, as it is forbidden to offer diseased or overage animals.(Compare Malachi 1,8 הקריבהו נא לפחתך, “just offer it to your governor!”) [The prophet reminds people that they would not dare offer a governor something less than first rate as he becomes aware of it immediately and will feel insulted. Ed.]

בני אהרן, the Torah does not mean that other priests are not qualified, but used the sons of Aaron as examples of priests in their prime. This corresponds to what the Talmud stated in tractate Chulin folio 24, according to which priests have to retire from active service when their hands and feet have become red as a sign of weakness.